This invention relates generally to injection molding and more particularly to hot runner apparatus having improved cooling provided by the circulation of cooling fluid through spaced openings in a front portion of an elongated core.
The cycle time of hot runner injection molding systems can be reduced by providing increased cooling to the cavity. Reducing cycle time by even a fraction of a second is very important in large volume applications such as making closures with millions or even billions of moldings. As seen in U.S. Pat. No. 5,094,603 to Gellert which issued Mar. 10, 1992, it is well known to provide the mold with a cooled core by circulating cooling water through a central cooling tube in the core. While this is satisfactory for many applications, there is still a considerable delay in the molding cycle before the mold is opened for ejection waiting for the melt to solidify. As the front portion of the cooled core forms part of the cavity, improved cooling must be achieved without unduly reducing the structural strength of this front portion of the cooled core.
Accordingly, it is an object of the present invention to at least partially overcome the disadvantages of the prior art by providing a cooled core with spaced openings in a front portion through which cooling fluid is circulated to improve cooling to the cavity.
To this end, in one of its aspects, the invention provides an injection molding hot runner apparatus having one or more heated nozzles seated in a cooled mold to convey melt to a gate leading to a cavity. The mold has one or more cooled cores having an elongated body portion, a central bore, and a front end. The cooled core has a front portion having an outer surface forming one side of the cavity extending around the front portion of the cooled core. The cooled core has a central cooling tube extending in its central bore with a first cylindrical space extending between the cooling tube and the surrounding body portion. The central cooling tube has an open front end inside the front portion of the cooled core, whereby a cooling fluid circuit is provided extending inside the cooling tube and along the first cylindrical space outside the cooling tube to cool the cooled core. The improvement comprises the front portion of the at least one cooled core having a number of spaced openings extending outwardly therein through which the cooling fluid circuit extends. Each opening has an inner end and an outer end. The inner end of each opening is located adjacent the open front end of the cooling tube to receive cooling fluid therefrom. The outer end of each opening is connected by rearwardly and inwardly extending cooling fluid flow means to the first cylindrical space extending rearwardly between the cooling tube and the surrounding body portion of the cooled core.
Further objects and advantages of the invention will appears from the following description taken together with the accompanying drawings.